This invention relates in general to metallic rod products intended to be drawn into wire, and in particular to a metallic rod product having an intentionally textured surface and to the preparation of such product.
Metallic wire products are conventionally manufactured by a wire-drawing process in which a metallic rod product having a relatively large initial diameter is pulled through one or more wire-drawing dies, with the result that the rod is elongated and reduced in diameter to the desired diameter of the wire product. Drawn wire is typically produced in the foregoing manner from rod product which previously may have been manufactured in a continuous process including a continuous casting apparatus and a rolling mill for working and shaping the cast rod to a desired metallurgical state and physical configuration appropriate for subsequent wire-drawing utilization. Specific details of apparatus and processes for the manufacture of metallic rod products, such as copper rod and aluminum rod, are well known to those skilled in the art. Such processes are disclosed in U.S. Pat. Nos. 3,315,349; 3,561,105; 3,623,532; 3,500,811; and need not be repeated herein.
Those skilled in the art recognize that the act of drawing the rod through a wire-drawing die to elongate the rod causes the generation of very substantial frictional forces acting on the die and on the rod at the point of movement through the die. It is desirable to reduce this frictional wire-drawing die force as much as possible, inasmuch as the frictional force causes the expensive wire-drawing dies to wear, and consumes substantial amounts of power.
It has been considered in the prior art that rod products intended for use in wire drawing especially to make electrical conductor wires should have a very clean, smooth, shiny exterior surface, since it was believed that the smoothest practicable surface on the rod would best minimize friction when the rod was pulled through a wire-drawing die. The production of rod intended for wire drawing, accordingly, included manufacturing techniques necessary to produce rod having the very smooth surface heretofore considered essential for the reduction of friction in subsequent wire drawing. A smooth finish may be imparted to the rod product, for example, by passing the rod through one or more sets of rolling mill rolls which have very smooth, finely polished rolling surfaces to impart a smooth exterior surface to the rod product. It will be understood that the rolls used in rolling the rod product to a smooth shiny finish will undergo normal wear; such rolls routinely are replaced or reconditioned as soon as imperfections appear on the polished surface of the roll, since such imperfections would fail to produce the smooth polished surface heretofore considered necessary in a rod product intended for wire drawing operations.
In the event that the metallic rod is intended to be drawn into a small electrical conductor wire, it is often deemed desirable to shave the surface of the rod to remove any surface defect or contamination. This shaving produces an extremely slick and smooth surface which is known to increase the wear rate of the wire drawing dies.
One method considered, prior to the present invention, as a possible solution to some of the aforementioned problems was similar, in some basic respects, to a cleaning method disclosed by J. W. Leighton in U.S. Pat. No. 2,239,044. However this method, which involved shot-peening the rod to form shallow depressions on the surface, was rejected in favor of the present invention because of serious deficiencies in that method and additional unexpected benefits gained with the present invention.
The major deficiency with the prior method is that shot-peening the rod directly produces only shallow and rounded depressions in the surface. It is well known that in general the capillary forces acting to draw a liquid into a pit are much greater when the pit or depression is relatively narrow and sharp (i.e., where the walls of the pit form a sharp angle with the surface). It is also obvious that shallow depressions do not have sufficient volume to hold a large quantity of liquid.
Another deficiency to shot-peening is that it raises a ridge, however slight, around the edge of the depressions which are likely to cause a defect during subsequent drawing of the rod by either shearing off in the drawing die or becoming folded over by the die causing slivers on the wire. This draw-back could possibly be avoided by a secondary smoothing operation, but subtracts from the simplicity of the method.
Still another deficiency is that shot-peening introduces stresses in the surface layers which reduces the ductility of the metallic rod and increases its strength. While the increased strength may be desirable, the reduced ductility increases the force necessary to deform the rod into wire.
A further deficiency is that there is a probability that some shot will become embedded into the surface, especially when peening ductile metal rods such as aluminum or copper. These embedded shot will cause a most serious defect if the rod is intended to be formed into electrical conductor wires.
Still another deficiency of shot-peening is that it is difficult to control the distribution or spacing of the depressions formed by shot-peening, especially when trying to peen a continuous metallic rod moving at speeds greater than 2000 feet per minute.
Related prior art processes are disclosed in U.S. Pat. Nos. 3,956,915, 2,078,434 and 3,136,054.
According to the present invention, it has been discovered that superior wire drawing and other benefits are obtained if the metallic rod product is intentionally provided with a certain textured surface, (i.e. striated) rather than with the smooth surface heretofore considered to be essential. The provision of striae on the exterior surface on the rod is believed to allow the rod, when used in a wire drawing operation, to pick up or entrain the drawing lubricant normally used in wire drawing, as the rod is pulled into and through the first few wire drawing dies. At least some of this entrained lubricant is carried into the dies along with the rod, thereby lowering the wear on the drawing dies and reducing the amount of force required to pull the rod through the dies. According to the present invention the exterior surface of the rod product is roughened by providing certain specifically sized and shaped indentations or striations in the rod surface, more or less uniformly distributed along and about the surface. The intentionally textured surface of the rod product preferably should consist only of narrow, interrconnected depressions in the surface and should exclude high, free standing protrusions since protrusions on the surface of the rod product tends to be sheared off in the drawing dies, causing metal slivers and other defects in the wire.
Accordingly, it is an object of the present invention to provide an improved metallic rod product useful for forming into wire.
It is another object of the present invention to provide an improved process and apparatus for producing a metallic rod product useful for forming into wire.
It is still another object of the present invention to provide an improved process for forming wire by using a novel metallic rod product in combination with a wire drawing machine.